1. Field of the Invention
This invention relates to a current source for utilization in integrated circuits and, more particularly, to a current source for providing a current, the magnitude of which increases with increasing temperatures.
2. Description of the Prior Art
Current sources having positive temperature coefficients find many applications in integrated circuits. For example, potential applications for current sources having positive temperature coefficient can be found in monolithic operational amplifiers, temperature references, voltage regulators and many other linear integrated circuit applications requiring temperature compensation.
A general method utilized in the prior art to generate a zero temperature coefficient voltage reference uses the negative temperature coefficient of an emitter-base voltage in conjunction with the positive temperature coefficient of an emitter-base voltage differential of two transistors operating at different current densities to make a zero temperature coefficient reference. The aforedescribed circuit is generally known in the art as a band gap regulator.
For another prior art application, using similar techniques as discussed above, a current source having a particular temperature coefficient is used in a class AB operational amplifier stage of a monolithic circuit for setting the idling current through the complementary transistor output pair to a constant value. The foregoing technique is utilized in the MC4558 operational amplifier manufactured by Motorola Inc. for instance.
Although the particular current source for the MC4558 works quite well, a tight specification must be held with respect to the magnitude of current generated by the current source. Additionally, because this current source operates as a current mirror and includes a pair of PNP transistors with one transistor thereof configured as a diode and having a resistor connected in series with the emitter thereof a tight matching tolerance is required so that the input current is correctly ratioed with respect to the output current.
Thus there is a need for a current source for applications in integrated circuits which has loosened requirements with respect to the components comprising the same and which is generally of less complexity with respect to prior art current sources.